It is believed that one of a golfer's principal concerns in perfecting his technique should be to minimise the sideways sway of a notional pivot point in the upper part of his body as he executes the backward and forward swing prior to striking the ball. It is further believed that this theoretically perfect position entails substantially no sideways movement of the eyes during the course of the swing, or at least a consistent slight eye movement characteristic of the golfer. It will be understood that the term "sideways" is being applied in relation to the golfer's torso and corresponds to a fore-and-aft movement relative to the intended line of travel of the ball. It is an objective of this invention to provide a novel device for the detection of self-movement which is especially adaptable as a sway detector for use in golf practice.